PECULIARITIES OF THE GRAVELS. 325 
LO 
origin as well as in lithological character, from the overlying softer and 
lighter colored materials. 
The theory of the blue lead so commonly held by the miners, namely, that 
a special stream deposited this kind of gravel,— which idea is also closely 
connected with another favorite one, namely, that this stream came from the 
north, —is so contrary to the whole mass of observed facts that it is not 
necessary to spend any time in refuting it, especially as this has been satis- 
factorily done by Mr. Goodyear* in another part of this volume. What we 
have to do is, to set forth as far as possible what are the differences in char- 
acter and position between the red and blue gravels, and to endeavor to 
account for the phenomena, which, however, as must be admitted, present a 
considerable number of points by no means easy of explanation. 
The essential facts in regard to the blue gravel are these: Wherever there 
is a heavy deposit of gravel, the lower portion of it is likely to be solidly 
compacted together, often to such an extent as to require the use of powder 
to loosen it so that it can be acted on by the hydraulic jet ; indeed, it some- 
times coheres so firmly as to require to be passed under the stamps, in order 
to break it apart. The writer cannot recall any instance where the blue 
gravel, if present at all, was not found underneath the red variety. But the 
relative thickness of the two varieties is by no means constant. At some 
localities a large part of the deposit is blue; at others, only a thin stratum 
has that character. Often, especially in cases where the gravel is thin, it 
is all soft and red; but asa general rule, where there is a wide channel, 
with, as is often the case, a narrower, deeper trough or “ gutter,” — to use 
the Australian term,— the gravel filling this deeper portion is very apt to 
belong to the blue variety. Of course this kind of gravel is not limited to 
any special altitude above the sea-level; its position is always related to that 
of the whole mass to which it belongs. 
There is another important fact connected with the occurrence together 
of the blue and red varieties of gravel.’ The line of division between them is 
usually perfectly well-marked, but irregular in position, that is, not coinciding 
with the planes of stratification; neither is it limited by any peculiarities in 
the lithological character of the gravel itself. Sometimes, indeed, a portion 
of one and the same boulder belongs to the red, and the other portion to the 
blue variety. In short, it is apparent that we have, in the phenomena in 
question, a case of chemical decomposition, proceeding from above down- 
* See Appendix B. 
